GB1589750A

GB1589750A - Stabilizers for photothermographic constructions

Info

Publication number: GB1589750A
Application number: GB41676/77A
Authority: GB
Original assignee: Minnesota Mining and Manufacturing Co
Current assignee: 3M Co
Priority date: 1976-10-07
Filing date: 1977-10-06
Publication date: 1981-05-20
Also published as: US4108665A; JPS5346020A; DE2745048A1; JPS6143701B2; FR2367301B1; FR2367301A1

Description

PATENT SPECIFICATION ( 11) 1589750

0 ( 21) Application No 41676/77 ( 22) Filed 6 Oct 1977 U ( 31) Convention Application No 730 678 ( 19) ( 32) Filed 7 Oct 1976 in C ( 33) United States of America (US) hf: ( 44) Complete Specification published 20 May 1981 ( 51) INT CL 3 GO 3 C 1/34 ( 52) Index at acceptance G 2 C 217 244 27 Y 302 304 30 X 310 315 333 362 371 372 380 C 19 E 2 A C 19 Y ( 54) STABILIZERS FOR PHOTOTHERMOGRAPHIC CONSTRUCTIONS ( 71) We, MINNESOTA MINING AND MANUFACTURING COMPANY, a corporation organised and existing under the laws of the State of Delaware, United States of America, of 3 M Center, Saint Paul, Minnesota 55101, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly 5 described in and by the following statement:-

This invention relates to photothermographic materials.

Photothermographic sheet constructions usually comprise a light-sensitive silver source (e g, an organic silver salt such as silver behanate or silver benzimidazole, or a complexed silver salt) in catalytic proximity to photographic silver halide A thermo 10 graphic developing agent, that is a reducing agent for silver ion, is also present in the construction Light ilmaging generates a latent image on the silver halide material.

This latent image is essentially the same as a latent image on conventional photographic processes and comprises stable groups of silver metal atoms formed on the silver halide by the action of the imaging light It is well known that the presence of silver metal is 15 autocatalytic to the reduction of silver ions in electronic proximity (near enough to allow electron transfer) to the silver metal The formation of the latent image on the silver halide thus generates catalytic silver sites which are in catalytic proximity to the thermographically developable silver source and will catalyze the thermographic reaction Upon heating the sheet with these catalytic silver sites present therein, thermo 20 graphic development (reduction of the silver source by the reducing agent for silver ions under the impetus of heat) occurs very rapidly about the catalytic sites and very slowly if at all, where the silver source is not catalytically activated A negative image is thus produced, with optical densities generated in light struck areas.

A significant problem with this technology has been the fact that the silver halide, 25 silver source, and reducing agent in non-light struck areas still remain active in the sheet after thermographic development After prolonged exposure of the final photothermographic image to light, the silver halide will have been converted almost completely to silver metal and catalytic sites will be present over the entire sheet Even at room temperature, the presence of the catalytic sites will be sufficient to cause the 30 non-imaged background areas to progressively generate a spurious image This spurious image is formed by the slow activity of the reducing agent acting at ambient temperatures on the catalyzed silver source Theoretically, the entire sheet would eventually darken completely, destroying the original image In fact, photothermographic sheets do show intolerable rises in Dmins and general discoloring after years of 35 prolonged and intense exposure to radiation.

Previous attempts have been made to stabilize the final photothermographic silver image, but these attempts have met with mixed success United States Patent Specification No 3,707,377, for example, discloses the use of halogen containing organic compounds as dry silver stabilizers A test is presented for distinguishing useful 40 halogen containing compounds from useless material This test characterization has proved to be wrong, with significant numbers of useful halogen containing organic compounds excluded by the test and numerous otiose materials included by the test definition Although the actual compounds tested in that patent performed properly according to that test, extrapolation beyond those compounds proves to be an error 45 The degree of stabilization provided by those compounds is also not as great as desired.

United States Patent Specification No 3,874,946 discloses the use of a tribromomethane sulphonylbenzthiazole as a stabilizer for dry silver sheet This compound generally works well as a stabilizer in photothermographic constructions, the benz 5 thiazole radical being well known as a photographic stabilizer.

It is an object of the present invention to provide photothermographic materials containing new stabilizers.

Therefore according to the invention there is provided a photothermographic imaging layer comprising a light-insensitive reducible silver source, photographic silver 10 halide in catalytic proximity to the reducible silver source, a reducing agent for silver ion, a binder and a stabilizing amount of at least one stabilizing compound of the formula:

CR Br:CR'R 2 R' (I) in which: 15 R represents a bromine or chlorine atom, R' represents a hydrogen atom or an alkyl, phenyl or naphthyl group each of which may be substituted, R 2 represents a hydrogen atom or an alkyl or phenyl group each of which may be substituted, and 20 Rs represents OH, an optionally substituted alkoxy group, trihydrocarbylsiloxy, carbamate group (as defined herein), sulphonate group (as defined herein), carbonate group (as defined herein), phosphate group (as defined herein) or carbozylate group (as defined herein).

Preferred stabilizing compounds are those of the formula 25 C Br 3 CH 2 R 3, and R 2 CH-Rs Br.

in which R 2 and R' are as defined above.

The stabilizing compounds may be added at any time to the photothermographic material to stabilize the image, but are best added into the original construction of 30 the sheet during coating of the emulsion.

The term carbamate as used herein refers to the group:

O H -OC 2 which is attached to the 1-carbon atom of the structural formula (I) through the oxygen bond Preferably an aryl, alkyl, alkenyl or heterocyclic group completes the valence requirements of the nitrogen atom in the carbamate group Alkyl includes 35 straight, branched and cyclic alkyl groups Aryl and alkyl groups are most preferred, having no more than 20 and 30 carbon atoms respectively.

Similarly the terms sulphonate, carbonate, phosphate and carboxylate used herein refer to the groups:

O O O O II II II II (-OS-), (-O-C-O-), (-OPO-) and (-OC), 40 11 O 0 lIo respectively, each of which groups is attached to the 1-carbon atom of the structural formula (I) through an available oxygen bond Aryl of no more than 20 carbon atoms is most preferred for satisfying the valence requirements of the sulphonate group, and aryl, alkyl, alkenyl, and heterocyclic groups ( 5-, 6-, or 7-membered rings of C, N, O and S ring atoms only) are preferred groups for the other groups 45 The ordinarily skilled phototbermographic artisan would realise the inherent limitation on the scope of these groups in excluding such terminating groups as are known to increase development in non-imaged areas by providing active development functionality Such groups include phenols and primary amines which are known active developers and which would not be suitable as substituents in the practice of the 50 1,589,750 present invention Excepting this limitation, the terminating portion of the compounds of this invention is not critical Only preferences are displayed in the practice of this invention by alteration of the end group structure, all inactive development end groups displaying a stabilizing capability.

Although 2,2,2-tribromoethanol is less reactive than ethanol in nucleophilic 5 reactions, its derivatives can be made in a similar manner to those of ethanol utilizing synthetic procedures that are commonplace to those skilled in the art For example, urethanes may be prepared by condensation of isocyanates and tribromoethanol in a suitable solvent; and esters may be prepared by the condensation of carboxylic acid halides and tribromoethanol All the materials may be prepared by condensation of 10 the appropriate reactants Some of these materials have been made in the prior art by these processes.

The stabilizers of this invention are found to perform well in all types of photothermographic constructions, on coated paper, on transparent film, with long chain fatty acid silver salt sources e g silver behenate, thermographically developable silver 15 salts, e g silver benzimidazole, and complexed silver salts, e g as disclosed in British Patent Specification No 1547225, and with in situ halidisation, e g as disclosed ill

United States Patent Specification No 3457075, or preformed silver halide, e g as disclosed in United States Patent Specification No 3839049 The use of stabilizers of the present invention has been found to be compatible with other photothermo 20 graphic additives such as toning agents and reducing agents disclosed in United States Patent Specification Nos 3392020, 3446648, 3667958, 3667959, 3672904, 3679426,

3751249, 3751252, 3751255, 3801321 and British Patent Specification Nos 1, 163,187,

3782,941 and 3794488 Sensitizers and sensitizing dyes as disclosed in United States Patent Specification Nos 3679422, 3666477, 3761279 and 3719495 are also useful, 25 as are such materials described as image amplifiers in United States Patent Specification

No 3708304, colour couplers in United States Patent Specification No 3531286, development inhibitor releasing compounds in United States Patent Specification No.

3700457, decolourizable light absorbers in United States Patent Specification No.

3745009 and mercury compounds disclosed in United States Patent Specification No 30

3589903 Processes and structures disclosed in United States Patent Specification Nos.

3748137, 3761270, 3764328, 3764329, 3769019, 3589901, 3152904, (Reissue No.

26,719), 3607282, 3685993, 3679414, 3218166 and 3756829 are also contemplated in the practice of the present invention.

The invention will now be illustrated by the following Examples 35 Examples.

A control or standard photothermographic emulsion was constructed to provide an appropriate environment for evaluation of the stabilizers of the present invention.

The control was constructed as follows.

A homogeneous mixture of 27 6 g silver behenate, 2 0 ml N-methyl-2pyrolidone 40 (sensitizer), and 3 0 g polyvinyl butyral in 172 4 g of a solvent solution ( 68:25:7) of methylethyl ketone, toluene, and methylisobutyl ketone was mixed for 20 minutes with 0 48 g of tetrachlorophthalic anhydride in 12 ml of ( 1:1 by volume) methylethyl ketone and methanol This was then mixed with 33 g of polyvinyl butyral and then 3 3 ml of a mercury bromide solution ( 10 g Hg Br 2/100 ml methanol) To this was 45 further added 2 6 ml of a sensitizing dye solution in methanol, the dye having the structure S CH-CH N C 2 H 5 6 5 and the solution having 0 262 g dye/100 ml methanol.

This final mixture was knife-coated on polyester film base at a 4 mil wet coating thickness, then forced air dried at 180 F ( 810 C)for four minutes 50 The second trip coating of the control comprised 200 ml methylethyl ketone, 13.0 g cellulose acetate, 0 6 g phthalazine (toner), 2 0 g 2,2 'methylene-bis-( 4-ethyl6-tert-butyl phenol), 2 0 g bis l 2,2 '-dihydroxy-3,3 ',5,5 '-tetramethyl diphenyll-l 2,4,41,589,750 trinethoxy pentyllmethane, 18 0 ml methanol, 18 0 ml acetone, and 0 5 g 4methyl phthalic acid.

A control photothermographic construction (without stabilizer) was formed by coating this second final mixture over the already coated polyester base The second coating was also knife-coated at a 4 mil wet coating thickness and dried at 180 F ( 81 C) for 3 minutes Imaging was performed by exposure to a tungsten light source and heat-processing in an inert fluorocarbon bath for 20 seconds at 260 F The imaged film strips were then exposed to 1000 foot candles for 24 hours under a fluorescent lamp The Dmin for each sample was measured before and after exposure to the fluorescent light.

In the compared photothermographic constructions, different amounts of stabilizer were added to the second coating prior to its application to the already coated polyester sheet The results are tabulated below.

Conc Dmin Dmin Compound Moles (wt %) (Initial) (Final) None 0 07 0 20 2,2,2-tribromoethanol 0 0011 0 3 0 06 O 08 0.00007 0 02 0 06 0 16 0.0071 2 0 0 07 O 07 2,2,2-tribromoethyl cyclohexanecarbamate O 0015 0 6 0 07 O 10 2,2,2-tribromoethyl benzenecarbamate 0 0015 0 6 0 06 0 08 2,2,2-tribromoethyl benzoate 0 0016 0 6 0 06 0 12 2,2,2-tribromoethyl ethylcarbonate 0 0017 0 6 0 09 0 11 Materials of similar structure but having perchloro groups in place of the perbromo groups were investigated but found to have insignificant effects upon stability.

Conc Dmin Dmin Compound Moles (wt %C) (Initial) (Final) 2,2,2-tribromoethanol 0 0141 4 0 0 06 009 1,1,1-trichloropropanol-2 0 0012 0 2 0 06 0 18 1,1,1-trichloropropanol-2 0 0122 2 0 0 07 0 24 2,2,2-trichloroethanol 0 0013 0 2 0 06 0 20 2,2,2-trichloroethanol 0 0134 2 0 0 07 O 22 1,589,750 A second control emulsion was formulated as above to evaluate further stabilizers of this invention The results are tabulated below:

Conc Dmin Dmin Compound Moles (wt %) (Initial) (Final) Control 0 08 0 46 2,2,-dibromo-2-chloro-1phenylethanol 0 003 1 0 0 08 0 15 tribromoethylcinnamate O 002 1 0 0 08 0 16 2-methyl-1, 1,1-tribromo-2propanol 0 003 1 0 0 08 0 13 Bi s( 2,2,2-tribromoethoxy)diphenylmethane O 0014 1 0 O 07 0 19 A third control emulsion was formulated as above The results are as follows:

Conc Dmin Dmin Compound Moles (% wt) (Initial) (Final) Control 0 08 0 28 p-toluenesulphonyl tribromoethyl urethane O 010 0 5 0 08 0 26 A fourth control emulsion was formulated as above The results are as follows:

Conc Dmin Dmin Compound Moles (% wt) (Initial) (Final) Control 0 06 0 17 2,2,2-tribromoethyl stearate 0 0004 O 2 O 09 0 09 0.0018 1 0 0 07 0 11 0.0054 3 0 0 09 0 11 1,589,750 X 1,589,750 A fifth control emulsion was formulated as above The results are as follows:

Conc Dmin Dmin Compound Moles (% wt) (Initial) (Final) Control 0 07 0 21 2,2,2-tribromoethyl-2furoate O 0 0013 0 5 0 09 0 10 Br 3 CCH 20 CO 0Bis( 2,2,2-tribromocthyl) succinate 0 0008 0 5 0 09 0 12 2,2,2-tribromoethy l benzenesulphonate 0 0011 0 5 0 07 0 D 8 2,2, 2-tribromoethoxytrimethyl silane 0 0014 O 5 0 08 0 11 2,2, 2-tribromo 1phenylethanol 0 0056 2 0 0 08 0 06 A sixth control emulsion was formulated as above The results are as follows:

Conc Dmin Dmin Compound Moles (% wt) (Initial) (Final) Control 0 08 0 25 2,2,2-tribromoethyl diphenylphosphate 0 006 3 0 0 08 0 08 The above examples show a general stabilizing effect for all derivatives of 2,2dibromo-2-cbloroethanol and 2 2,2-tribromoethanol derivatives The variation in the sensitometric properties of the different controls is the result of irregularities produced by small batch processing In all instances, however, the compounds of this invention displayed measurable stabilizing functionality.

Although manufacture of compounds of the present invention is well within the skill of the artisan, as described above, the following two examples describe specific processes for synthesizing these compounds Preparation of 2,2,2-tribromoethyl cyclohexylurethane-Typical Urethane Preparation.

To a solution of 5 6 g of 2,2,2-tribromoethanol in 8 ml of toluene was added 2.5 g of cyclohexyl isocyanate and 1 drop of triethylamine The resultant solution was allowed to stand at room temperature for several days until a significant amount of white precipitate had formed The white precipitate was isolated by filtration and washed with cold toluene to give the urethane derivative of 2,2,2tribromoethanol.

Preparation of 2,2,2-tribromoethyl stearate -Typical Ester Preparation.

28.27 g of 2,2,2-tribromoethanol was dissolved in dichloromethane and 7 9 g of pyridine was added as one portion To this mixture was added 30 3 g of stearoyl chloride The resultant mixture was allowed to stand overnight during which time a white precipitate iad formed The precipitate was removed by filtration, and the dichloromethane solution was washed once with saturated aqueous NAHC Os and twice with water, then dried (with Na SOJ) Removal of the dichloromethane under reduced pressure gave the ester as white crystals that could be purified by recrystallization from a hexane-ethyl acetate solution.

As shown by the above examples, a wide latitude in the concentration of the stabilizers is useful Both lower and upper limits are difficult to fix as exact values 5 In a commercial embodiment it is believed that the stabilizers should be present in a range of 0 02 to 5 0 % by weight of the imaging layer (the photothermographic emulsion layer) A preferred range would be 0 05 to 4 0 % by weight of the emulsion layer.

Conventional thermographic and photothermographic binder materials are useful 10 in the practice of this invention Such transparent binders are usually natural resins, synthetic polymers, or mixtures thereof such as gelatin, polyvinyl butyral, celluloxic esters, polyesters, vinyl resins, carbonates, acrylic resins, or any other of the many known polymers known in the art as useful in photothermographic sheets.

The molecular weight of substituents on the stabilizers is believed to be without 15 criticality to the functionality of the tribromoethanol derivatives of the present invention, with even the stearic acid derivative showing excellent properties The provision of limitations on the size and weight of these terminating groups is therefore based upon economic and rational limitations as opposed to functional requirements Alkyl groups, for example, as described for RI, R 2, and R 3 may be of any size One would 20 choose to limit the size only because it is unnecessary to make the stabilizer larger.

Such characteristics as solvency and non-diffusiveness within the emulsions are known to be effected by the character and size of terminating groups without affecting the utility of the materials The preferred size ranges now described are to be considered in this light 25 The alkyl and alkoxy groups described for RI, R 2, and R 8 are preferred to have no more than 30 carbon atoms Such well known and accepted substituents on these grouns (alkyl, alkoxy, aryl, heterocyclic or alkenyl) as are known in the art to be acceptable on additives to photographic and photothermographic systems such as halogen atoms, cyano groups, sulfonic acid groups, carboxylic acid groups, alkyl or 30 alkoxy groups (e g, as additions on aryl or heterocyclic groups) may be present without affecting the utility of the stabilizers Such groups could be used, for example, to adjust solvency characteristics to make the stabilizers more compatible with particular binders as would be readily understood by the ordinarily skilled artisan.

Similarly the phenyl, naphthyl, aryl, alkenyl, hydrocarbyl, and heterocyclic groups 35 have no critical size limitations with regard to functionality Size limitations are presented only as rational preferences, not functional necessities The aryl groups may have aliphatic substituents thereon (as to form either alkaryl or arylalkyl groups) and the ring may have those substituents described above which are generally considered innocuous or beneficial In general, aryl groups would preferably have no more than 40 carbon atoms merely to reduce the weight of materials added No more than 20 carbon atoms in the aryl group would be more preferred, and phenyl and naphthyl most preferred Accordingly, alkenyl preferably have no more than 30, and more preferably at most 20 or 10 carbon atoms Heterocyclic rings of 5, 6, or 7 atoms (of only C, N, 0, and S ring members) are contemplated and preferably contain 45 only one heterocyclic ring and no more than one fused phenyl ring attached thereto (e.g, benzothiazole) Total atoms (excluding H) should be no more than 20 atoms in the heterocyclic group, including substituent groups like those previously discussed.

Claims

WHAT WE CLAIM IS:- 1 A photothermographic imaging layer comprising a light-insensitive reducible 50 silver source, photographic silver halide in catalytic proximity to the reducible silver source, a reducing agent for silver ion, a binder and a stabilizing amount of at least one stabilizing compound of the formula: CR Br C Rl R 2 RS (I) in which: R represents a bromine or chlorine atom, 55 RW represents a hydrogen atom or an alkyl, phenyl, or naphthyl group each of which may be substituted, R 2 represents a hydrogen atom or an alkyl or phenyl group each of which may be substituted, and R 3 represents OH, an optionally substituted alkoxy group, trihydrocarbylsiloxy, 60 carbamate group (as defined herein), sulphonate group (as defined herein) carbonate groun (as defined herein), phosphate group (as defined herein) or carboxylate group (as defined herein).

1,589,750

2 An imaging layer as claimed in Claim 1 in which the at least one stabilized compound is selected from C Br CH 2 R' and R 2 CH-Rs C Bra in which R 2 and Rs are as defined in Claim 1.

3 An imaging layer as claimed in Claim 2 in which the at least one stabilizing 5 compound has the formula:

C Br 6 CH 2 Rs in which R" is as defined in Claim 1.

4 An imaging layer as claimed in Claim 1 or Claim 2 in which the at least one stabilizing compound is present in an amount constituting 0 025 to 3 % by weight 10 of the imaging layer.

An imaging layer as claimed in any preceding claim in which the stabilizing compound is 2,2,2-tribromethanol.

6 A photothermographic imaging layer as claimed in Claim 1 substantially as 15 herein described with reference to the Examples.

7 A sheet carrying a photothermographic imaging layer as claimed in any preceding claim.

Agents for the Applicants:

LLOYD WISE, TREGEAR & CO, Chartered Patent Agents, Norman House, 105-109 Strand, London, WC 2 R OAE.

Printed for Her Majesty's Stationery Office by the Courier Press, Leamington Spa, 1981.

Published by the Patent Office, 25 Southampton Buildings, London, WC 2 A l AY, from which copies may be obtained.

1,589,750